1. Field of the Invention
This invention relates generally to a radio link control (RLC) status protocol data unit (PDU) format and, more particularly, to an enhanced RLC STATUS PDU format for use in a wireless communication network.
2. Description of Related Art
In current UMTS RLC specification, STATUS PDUs are specified to inform the sender RLC entity the acknowledgment information of the RLC AMD (Acknowledge Mode Data) PDUs received at the receiver peer entity. Based on the information, the sender decides to retransmit the negative acknowledged PDUs or to move its transmission window forward based on the procedure specified in the specification. The STATUS PDU could be event triggered or triggered based on the specified timer. The transmission of STATUS PDU should be on time in order to avoid the deadlock/stall situation of the transmission window at the sender peer entity.
In current E-UTRA RLC specification, segmentation of the RLC PDU is introduced. As shown in FIG. 1, the current format of the STATUS PDU consists of a STATUS PDU payload 11 and a RLC control PDU header 12. The RLC control PDU header 12 consists of a D/C field and a CPT field. The STATUS PDU payload 11 starts from the first bit following the RLC control PDU header 12, and it consists of one ACK_SN field and one E1 field, zero or more sets of a NACK_SN field, an E1 field and an E2 field, and possibly a set of an SOstart field and an SOend field for each NACK_SN, wherein the set of header combined with E1, E2, NACK_SN, SOstart, and SOend fields is used to indicate the missing segment of the AMD PDU. The descriptions of the fields are as follows:
D/C Field (Length=1 bit)
The D/C field indicates the type of PDU. Specifically, the PDU is a AMD PDU when D/C field=0, and the PDU is a control PDU when D/C field=1.
CPT Field (Length=3 Bits)
The CPT field indicates the type of control PDU. Currently, it is specified that the control PDU is a STATUS PDU when CPT field is 000.
Acknowledgement SN (ACK_SN) Field (Length=10 bits):
The ACK_SN field indicates the SN (sequence number) of the next not received AMD PDU which is not reported as missing in the STATUS PDU. When the transmitting side of an AM RLC entity receives a STATUS PDU, it interprets that all AMD PDUs up to but not including the AMD PDU with SN=ACK_SN have been received by its AM RLC entity, excluding those AMD PDUs indicated in the STATUS PDU with NACK_SN and portions of AMD PDUs indicated in the STATUS PDU with NACK_SN, SOstart and Soend.
Extension Bit 1 (E1) Field (Length=1 Bit):
The interpretation of the E1 field is to indicate that a set of NACK_SN, E1 and E2 does not follow when E1 is 0, and to indicate that a set of NACK_SN, E1 and E2 does follow when E1 is 1.
Negative Acknowledgement SN (NACK_SN) Field (Length=10 Bits)
The NACK_SN field indicates the SN of the AMD PDU (or portions of it) that has been detected as lost at the receiver.
Extension Bit 1 (E1) Field that Follows the Aforementioned E1 Field of 1
Extension Bit 2 (E2 ) Field (Length=1 Bit)
The interpretation of the E2 field is to indicate a set of SOstart and SOend does not follow when E2 is 0, and indicate a set of SOstart and SOend does follow when E2 is 1.
SO (Segmentation Offset) Start (SOstart) Field (Length=15 Bits)
The SOstart field (together with the SOend field) indicates the portion of the AMD PDU with SN=NACK_SN (the NACK_SN for which the SOstart is related to) that has been detected as lost at the receiving side of the AM RLC entity. Specifically, the SOstart field indicates the position of the first byte of the portion of the AMD PDU in bytes within the data field of the AMD PDU.
SO End (SOend) Field (Length=15 Bits)
The SOend field (together with the SOstart field) indicates the portion of the AMD PDU with SN=NACK_SN (the NACK_SN for which the SOend is related to) that has been detected as lost at the receiver. Specifically, the SOend field indicates the position of the last byte of the portion of the AMD PDU in bytes within the data field of the AMD PDU. A special SOend value “111111111111111” is used to indicate that the missing portion of the AMD PDU includes all bytes to the last byte of the AMD PDU.
With the above STATUS PDU format, the receiver RLC entity may inform the sender RLC entity the acknowledgment information of the RLC AMD PDUs received at the receiver. For example, when a sender transmits ten AMD PDUs with SN=1 to 10 to a receiver and the AMD PDU with SN=2 and the 10-40 bytes portion of the AMD PDU with SN=3 are not received at the receiver, the receiver will respond a STATUS PDU as follows for indicating the missing of AMD PDU:
D/C=1
CPT=000
ACK_SN=1
E1=1
- - - indicating missing PDU with SN=2
NACK_SN=2
E1=1
E2=0
- - - indicating missing 10-40 bytes of PDU with SN=3
NACK_SN=3
E1=0
E2=1
SOstart=10
SOend=40
Another example is given as follows to further demonstrate the use of the STATUS PDU. A sender transmits ten AMD PDUs with SN=1 to 10 to a receiver and the AMD PDU with SN=2 and the 10-40 bytes portion and 100-120 bytes portion of the AMD PDU with SN=3 are not received at the receiver. The receiver will respond a STATUS PDU as follows for indicating the missing of AMD PDU:
D/C=1
CPT=000
ACK_SN=11
E1=1
- - - indicating missing PDU with SN=2
NACK_SN=2
E1=1
E2=0
- - - indicating missing 10-40 bytes of PDU with SN=3
NACK_SN=3
E1=1
E2=1
SOstart=10
SOend=40
- - - indicating missing 100-120 bytes of PDU with SN=3
NACK_SN=3
E1=0
E2=1
SOstart=100
SOend=120
It can be seen that the aforementioned STATUS PDU may include two identical NACK_SN fields (NACK_SN=3) for indicating the same missing PDU (with SN=3). This causes a bandwidth waste, as duplicated NACK_SN fields are included in the STATUS PDU, which need extra 10 bits of data length. If the number of missing portions of the AMD PDU increases, the number of duplicated NACK_SN fields included in the STATUS PDU also increases, resulting in a serious bandwidth waste.
Therefore, it is desirable to provide an enhanced RLC STATUS PDU format for use in a wireless communication network to mitigate and/or obviate the aforementioned problems.